[LiamSarsfield]

Proposed changes

• On the modern Settings page, the collapsed "Cornerstone pages" group now shows its one-line description in the header ("Choose the pages that matter most on your site so Boost can give them its most targeted optimizations."), like the other groups. Before, it only showed after expanding.
• The text goes through the same Group description slot as the other groups. The header button's aria-describedby now points at it, and its accessible name stays "Cornerstone pages".
• It reuses the legacy dashboard's existing string, so it needs no new translation. The fuller explanation inside the body is unchanged.
• The legacy dashboard is unaffected. Its rendered HTML is byte-identical before and after, and screenshots at 1280 and 782 px, LTR and RTL, match pixel for pixel.

Screenshots

Modern Settings, "Cornerstone pages" collapsed. Below the new line, the after image is the before image shifted down 32 px, pixel for pixel.

	Before	After
LTR, 1280 px
RTL, 782 px

Related product discussion/links

• Follows Boost: Organize modern settings into collapsible sections #52562 (collapsible sections) and Boost: Describe Cornerstone Pages under its title on the legacy settings page #52498 (legacy one-liner).

Does this pull request change what data or activity we track or use?

No.

Testing instructions

• Enable the modern dashboard with the rsm_jetpack_ui_modernization_boost filter and open Boost > Settings.
• With "Cornerstone pages" collapsed, confirm the description shows under the title and page summary, in LTR and RTL at desktop and narrow widths.
• Expand it and confirm the body still shows the fuller explanation.
• With a screen reader, focus the header button and confirm it reads the name, then the description.
• pnpm test app/assets/src/js/pages/settings in projects/plugins/boost: the new test finds the collapsed header button by that description.

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[jp-launch-control]

Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

Full summary · PHP report · JS report

[xavier-lc]

LGTM